The down pipe is just going to make everything more pronounced. If the catch back sounds like crap, then it will sound worse as a turboback. My personal opinion, billy boat, apr, nuespeed, Cts, they all sound good and you can't go wrong. Any setup is going to be much more farty and boisterous. It's just the result of increased airflow. Less restriction equals more noise.
2013 DBP GTI - Revotechnik Stage 2 - Neuspeed Catback - CTS catted Downpipe - Black Smoke Depo LED tails - Neuspeed Sport Springs - H&R 10mm spacers